Blood grouping of primate animals by our team reaches back to the use of monkeys in the discovery of the Rh factor in man by Karl Landsteiner and Alexander Wiener in 1940. The most productive period, however, began in 1963 under the tenure of the grant GM 12074 (1-12). During that time we were able to demonstrate in a large number of primate animal species, the existence of human-type blood groups, i.e., homologues of the A-B-O, M-N, Rh-Hr and Ii blood group systems of man, as well as of numerous simian-type blood groups, analogues to those of man, in primate animals most commonly used in research, i.e., chimpanzees, gibbons, baboons, rhesus and crab-eating macaques. We have presently available 25 simian-type reagents for blood grouping of rhesus and crab-eating macaques, 23 reagents for baboons and more than 20 for chimpanzees. The latter cross react also with gorillas. In addition, most of the Old World Monkeys and apes can also be tested for their human-type blood groups. Over the past several years, the services of our Blood Group Reference Laboratory have been used by numerous scientists who needed informaton for studies in experimental surgery (experimental heart and lung surgery, simian organ transplantation to man, cross-circulation with patients in hepatic coma, testing of the use of human umbilical vessels in transplantation, etc.), experiments to improve transfusion and blood preservation techniques, transfusion support for sick animals, field studies in native countries, breeding programs, etc. This activity has resulted in the nomination of our Laboratory as the WHO Collaborating Centre for Haematology of Primate Animals.